This is one of the best preserved regions as far as fauna, and especially, its excellent forest areas are concerned. The park is surrounded by the Central mountains of the Northern Iberian Mountain Range, in the region of Cameros, on the border of the province of Soria. In this protected space, there are some of the best examples of forests in the Iberian Mountain Range. The most outstanding natural forests are of wild pine, beech and Pyrenean oak groves, and other more exceptional species such as birches, groves of white oak, mountain holm oak groves and hooked pine. Lime trees, maple trees, service trees, whitebeams, mountain elms, yew trees, quaking aspen and ash trees also appear.
Among the mammals, it is worth mentioning species such as the fox, wild boar, deer, squirrel and mountain cat in the forests, and otter and Pyrenean muskat in the rivers. There are numerous species of forest birds of prey, such as the goshawk, the sparrowhawk, the honey buzzard, the booted eagle, the common buzzard and the short-toed eagle. Nocturnal birds can also be observed such as the long-eared owl and the tawny owl. The sierra is considered to be an area of international importance for the passage of migratory birds.